RATE OF LEAF PRODUCTION IN RESPONSE TO SOIL-WATER DEFICITS IN-FIELD PEA

Plant leaf area is critical for predicting the amount of radiation int ercepted by a crop, and thereby, for estimating dry matter production. Under soil water deficit conditions, plant leaf expansion is reduced as a result of both a reduction in the rate of leaf production (RLP) a nd in the rate of individual leaf expansion. Quantifying the effect of soil water deficits on plant leaf expansion depends in part on predic ting its effects on the timing of leaf production. The effect of soil water deficits on RLP was examined for three pea cultivars in greenhou se and field experiments. The level of soil water deficit was characte rized as the fraction of transpirable soil water (FTSW). A quantitativ e function between RLP and FTSW was established in greenhouse experime nts and was tested in independent pot and field experiments. A good co nsistency in this relationship across a diversity of experimental cond itions and cultivars was shown. The logistic function obtained represe nts an effective way to simulate the effects of soil water deficits on RLP, especially as FTSW could be estimated from a soil water balance. RLP was reduced only for FTSW < 0.2, and consequently, RLP was less s ensitive to soil water deficits than transpiration and leaf expansion. Soil water deficit induced a slight rise in canopy temperature due to stomatal closure. However, this rise in temperature for FTSW < 0.4 ca nnot account for maintaining RLP compared to the drop of transpiration and of leaf expansion rates observed for FTSW between 0.4 and 0.2, RL P can be considered independent of soil water content if FTSW > 0.2. I n the field, such level of soil water deficit inducing a decrease of R LP occurs generally only after the end of leaf production during the l ast reproductive stages of pea crop. Thus, except in situations of ext reme soil water deficit and on shallow soils, leaf production depends solely on air temperature. (C) 1998 Elsevier Science B.V. All rights r eserved.